Focussed microwave irradiation does not impair microdissection of rat brain nuclei, spinal cord and other tissues and allows the assay of the concentrations of chemicals which undergo rapid metabolism during postmortem processes. New microwave devices to inactivate enzymes in brain and other tissues of large animals and in free moving animals are needed. Such equipment would offer a unique possibility of measuring the effect of drugs on the steady state and turnover rate of neurotransmitters of metabolites during various stages of sleep.